Incandescent filament support and method



March 17, 1953 w. CURTIS INCANDESCENT FILAMENT SUPPORT AND METHOD Filed Oct. 10, 1950 INVENTOR. 01172 M C llrtis ATTORNEYS Patented Mar. 17, 1953 INCANDESCENT FILAMENT SUPPORT AND METHOD Lorin W. Curtis, Verona, N. J assignor to Tung- Sol Electric, Inc., a corporation of Delaware Application October 10, 1950, Serial No. 189,391

6 Claims. 1

This invention relates to incandescent lamps and more particularly to supporting means for the filament in the form of support wires that provide mechanical support for the filament as well as the means for the supply of electric power.

Ordinarily the legs of an incandescent filament are welded to the ends of the support wires by a resistance welding or embedding process. In this process the filament legs are welded to the weld pad which is a flattened portion on the end of the support wire, and it is preferable of course to embed the filament leg in this pad.

This type of supporting means for the filament has not been found to be entirely satisfactory, especially in high wattage, low voltage type miniature lamps such as those used for automotive lighting. It has been found that the filament legs may fracture at a point immediately adjacent the weld points long before the filament itself would actually burn out. It has also been found that due to the frequent heating and cooling periods encountered in night driving, the physical characteristics of the metal support wires become greatly changed and cause the filament leg to become loose and eventually fall out of actual contact with the support wire.

The heat generated by the filament that must be dissipated at the juncture of the filament leg and the support wire comes from three sources, (a) conduction through the legs of the filament, (b) convection through the gas atmosphere surrounding the filament, and (c) the heat generated because of the resistance of the weld and the high currents encountered particularly in low voltage automotive lighting. The greatest source of heat is of course that which is conducted to the weld through the filament legs.

The filament support means in accordance with this invention operates to by-pass that heat that would normally arrive at the weld through the filament legs around the weld and into the support wire. Actual tests have indicated that with this procedure much of the weld depreciation vanishes and the life of the lamp is greatly increased.

The above and other objects of this invention will become more apparent from the following description and accompanying drawings forming a part of this application.

In the drawings Fig. l is a side elevation of an incandescent lamp in accordance with the invention;

Fig. 2 is an enlarged view of the filament and supporting wires of the incandescent lamp shown in Fig. l to show mechanical and electrical connections between the filament legs and the support wires;

Fig. 3 is a perspective view of one form of the invention;

Fig. 4 is a cross-sectional view taken along the line 4-4 of Fig. 3;

Fig. 5 is a perspective view of another form of the invention;

Fig. 6 is a cross-sectional view taken along the line 6-6 of Fig. 6;

Fig. '7 is a perspective view of still another form of the invention; and

' Fig. 8 is a cross-sectional view taken along the line 88 of Fig. 7.

Although the invention will be described particularly in connection with automotive head lamps of the high wattage, low voltage type, it will be apparent that it is useful in other moandescent lamp applications wherein difiiculties are encountered in connecting the filament legs with the support wires.

With reference to Figs. 1 to 4, I denotes an incandescent lamp having a glass envelope 2, .a base 3, and electrical connectors 4 extending from the bottom of the base. Within the glass envelope 2 are a pair of filament support wires 5 and 6 extending upwardly from the glass press 1. These wires 5 and 6 also pass downwardly into the base 3 and are connected to two of the terminals 4. In double filament lamps all three of the terminals 4 would be used with one terminal being common to the two filaments. The filament 8 within the glass envelope 2 is formed with a pair of legs 9 and I0 welded, respectively, to the support wires 5 and 6. The weld points are denoted by the numerals H and I2 and are spaced from the inner ends of the support wires 5 and 6.

The inner ends of the support wires 5 and 8 are flattened as shown at l3 and I4 and are formed so that the legs 9 and I0 bear against these filattened portions when they are welded at points II and I2 to the support wires 5 and 6. That part of each filament leg between the flats l3, l4 and the welds ll, [2 is spaced from its support wire so that the gas within the lamp can circulate thereabout.

The invention can perhaps be more clearly seen in Figs. 3 and 4 of the drawings. Like numerals have been used to designate corresponding components in all figures. The support wire 5 is formed with the flattened portion 13 at the very end of the wire and with a second flat l5 spaced from the first flattened portion l3 and connected by a depressed flattened part IS. The

.lfl ame 1 Itis"important to note that thefilamentleg is not weldedor otherwise securely; fastened tdth'efla'tten'd.partl3 ofthc's'upportwir but is free to moverelative tothe flat to eliminate "stresses or strains that would be produced .by

is "merely provided; With fiat I 5 is preferably made slightly higher than the fiat [3 so that the filament leg 9 can be substantially wholly embedded in the fiat I5 during the formation of the weld II so that that part of the filament leg 9 overlying the fiat l3 will bear snugly against the flat l3 without any deformation of the filament leg part 9 between the flats l3 and I5.

With] this structure it hasv been found; that the major source of heat that normally causes failure of the weld, that is the heat arriving ;at the Weld by conduction through the filament leg 9, is by-passed by reason of the contactof the filament leg 9 with the fiat l3. A substantial part of the heat leaves the filament leg upon its contact with the fiat l3andtisithen, conducted around the weld and into thejsupport wire body 5.

This procedure has been foundmo'st efiect'ive in securing long lasting welds and extending the life of the lamp in most instances to that of the reasonof difierent ecoefficients of expansion of the filament l'eig material that is usually tungsten and the support wire material normally made of .1 Eigs. j5 and 6, which. illustrate a modification'of'th'e form of the invention. shown in Fig.

3, the fiat-l3 on the enfdfof the supportwire "5 is shaped in theform of a ,V, denoted by the numeral I'|,, to limit the,sidewisefmotionl of the 'outjs'etting'upl stresses orl'strains thatmay destroy invention wherein the endof the support wire, instead of ,being fiattenedas shown at I3, Fig'f3, .a' groove IB through iw ic'hjith fi ament l ejfl'p ssl il. Afmount for an incandescent lamp filament v1201 1 .r sin a wel n sur a formed on said jrnountfat a point spaced from one end thereof ;tachment of a filament legj-theretocomprising:

means spaced from the end ofithe-mount for welding attachment of the filament leg; and

means between the weld and said end of the mountucontacting the filament leg to conduct th eat therefrom.

3. The mount according to claim 2 wherein said-meansforcontacting the filament leg comrprisesta flattened part adjacent said end of the mount andbearing against the filament leg.

"4.The mount according to claim 2 wherein ,said contacting means comprises a V-shaped groove formed in said mount adjacent said end th r o or r ce on of th fi ment. vleg therein.

ffilamentand yet permit the leg 9 to expand "and c'ontractewithchan es temperature with- 5 The mount acc rding to claim 2 wherein said;v contacting means comprises a slot; formed i se dm u for recep o t e tfilamentle 25* therein.

6. Thevmethod of attaching the leg oftan incandescent filament to a mount, comprising welding the filament to the mount at, a'point spaced from one end thereof, and bringing the filament leg into heat conductive engagement with the mount at a point between the weld and the filament with'at least part of the legvbetweenthe weldand the point of heat conductive engagement-spaced from the support wire.

LORIN W. CURTIS.

-' REFERENCES CITED The following referencesare of record,in the file of this patent:

UNITED STATES PATENTS Number Name Date 473,208 Carey Apr. 19, 1892 605398 Michaelson June.14, 1898 2445 1 86 Meeker et al. Jan. 24, 1939 2,227,324 Severin Dec.'31, 1940 2 ,315,504 vCurtis Apr. 6,1943 

